text:
Does a lift to drag ratio of 100 imply an unattainable performance ratio of 1?
An answer to this question stated that a lift to drag ratio of 100 is "unachievable".
When thinking of ratios, they seem to always be a fraction of one thing to another, with the sum of them being the total amount of what is being compared.
For example a ratio of 1 to 4 means and apportionment of 1/5 and 4/5, 20% and 80%.
From this reference we can see that the DAE 21 airfoil exceeds a lift to drag ratio of 100.
It seems that, as an efficiency, lift to drag ratio (or any ratio) can not be expressed as anything other than:

fraction of a ratio = n/(n+1)

Yes, this can never equal 1.
Is this correct?

"to what extent are we, as responsible persons, required to correct the misunderstandings?"

Just another day in the office at the Aviation Stack Exchange website.

What's a performance ratio?

@sophit it was the phrase "jets have constant thrust, props have constant power" that piqued my interest.  But props can have closer to constant thrust by adjusting their pitch to the freestream velocity (maintaining efficiency).  Jets solve the problem by having their fans churn happily away in a duct away from the free stream.  Ha!

@RobertDiGiovanni That's not how it works... Jets accelerate a small mass to very high speeds, giving them a low propulsive efficiency at low speeds (where a propeller would have a high efficiency). The fact that their efficiency is low at low speeds is why it doesn't decrease much at high speeds. Also, at those speeds where a propeller can no longer accelerate the air (which it must to produce thrust), a jet can, because as stated earlier, jets accelerate small mass to very high speeds. While this restrains the efficiency at low speeds, it allows the jet to produce thrust at high speeds.

"constant power can approximate constant thrust if blade AoA is kept optimal" - not true. If you look at the chart given in this answer of mine, you can see that for a constant power, thrust decreases as speed increases. That graph is derived from the relationship $P=V⋅T$
.

@AdityaSharma again many thanks for your comments.  My study of Isp shows that there is more than "mass flow" with jets.  Just look at the cross section of the turbine blades.  Something Bleriot would have been familiar with in 1909.  And I do not see the need to carry power through propulsion.  Force moves objects.  So once force is applied (from any propulsion system) only drag will stop acceleration.  The neat thing I learned is how important efficiency is.  Proper pitch to the relative wind is essential.

"carry power through propulsion" what does that mean?

It means that that whatever the propulsion system is acting on (the airframe) is being moved by force.  All the bells and whistles on the engine no longer matter.  If prop efficiency is maintained, the "push" on the airframe can keep it accelerating beyond where a fixed pitch loses efficiency.  This was a major improvement in aviation.  120 knots became 320 knots.  Reducing drag improved top speeds even more.

You can keep a factor between 0 and 1 and express an infinite range of ratios. 0.51:0.49 (1.04:1); 0.99:0.01 ; 0.999996:0.000004 (249,999:1); 0.99009901:0.00990099(100:1 or the smaller quantity as a fraction of the total is 1/101, although with L:D such a scaler fraction is meaningless because you would be interested in the vector components)

"Proportion" was the word I was searching for earlier.
A ratio can be zero. My ownership ratio of personal jets to cars is 0:1.
The limits of a proportion are zero and one, as one side of the ratio approaches either zero or infinity with the other side held at any finite quantity. (calculus definition of limits)

@MaxPower 0 jets.  Well, have to start from somewhere ;-).  This originally grew out of the statement that a glide ratio of 100 was impossible, which has been corrected.

Terms can get kind of sloppy here. If you are truly talking about the ratio of Lift to Drag, it would be best expressed as a ratio of one number to another. If someone talks about a Lift to Drag ratio of "100", what they really mean is a Lift to Drag ratio of 100:1. This means that Lift/Drag = 100/1 = 100. Nothing unattainable about that.
So could we say that out of 101 mysterious "somethings", 100 of them are "Lifts" and 1 of them is a "Drag"? Sure, maybe, but that doesn't seem like a terribly useful concept, since we are talking about two orthogonal forces.
As opposed to saying that the ratio of Cats to Dogs is 5:2, for example -- here the sum of 5 + 2 = 7 would have some useful relevance, i.e. the actual total number of animals present in a sample size that had 5 cats...
Your question mentions a performance ratio.  It's not clear what this would be mean.  Are you making the mistake of thinking that a L/D ratio of 100/1 (i.e. 100) somehow has something to do with 100 percent?  That would be a misconception.
One can find sources on the internet (example) that imply that when a ratio is converted to a fraction, the denominator should reflect the total number of things present.  In other words, in the Cats-and-Dogs example above, we can say that the "Cat fraction" is 5/9 and the "Dog fraction" is 2/9.  But that's not what we mean we express an L:D ratio as a fraction.  When we talk about "L/D", we simply mean Lift divided by Drag.  If L/D is 100, then that simply means that Lift is 100 times greater than Drag, so Lift/Drag = 100/1 = 100.
Are you thinking that a Lift/Drag ratio of 100 somehow implies that (following the phrasing of the previous paragraph) the "Lift Fraction" is 100% or 100 /100, meaning that (Lift / (Lift + Drag)) = 1, and thus implying that Drag is zero?  That would be a misconception.

I’d read the question as suggesting that 100:1 is a practical limit, which seems plausible given that the highest performing sailplanes were still a little way short of this last time I checked, and presumably if anyone knew how to make a higher-performing glider then they would.

When people say that $L/D$ is a measure of aerodynamic efficiency -- they are using the word efficiency very loosely.  They are simply using it as a generic term for 'figure of merit'.
When people say that efficiency ($\eta=p_o/p_i$) can not be greater than 1.0, they are referring specifically to a precise definition of efficiency as the ratio of power out to power in.  Note that this engineering definition of efficiency does not apply to other quantities (mass, force, speed, time, money, etc.).
Usually this definition of efficiency is applied to power conversion and transmission devices.  Things like electric motors that convert electrical power to shaft power, propellers that convert shaft power to thrust power -- or wires and shafts that move power from one place to another.  These devices do not store energy.  They have an instantaneous state -- if power is going in, then power is coming out.
The fact that efficiency must be less than 1.0 is due to the laws of thermodynamics.  1) You can only break even ($\eta\le1.0$).  2) You can't even break even ($\eta<1.0$).
When we run a power conversion device 'backwards' (say using a motor in a generating mode, or using a propeller as a windmill), we must be careful to re-define what 'input' and 'output' means.  Losses like friction and resistance are always there of course.
For all of these devices, the 'inefficiency' ($1-\eta$) is a measure of the power lost to friction, resistance, drag, and other phenomena that eventually wind up as waste heat.  The first law tells us that $p_i=p_o+p_l$ -- the input power comes out as useful output plus losses.  This lets us write $\eta=p_o/(p_o+p_l)$.  Which (with $p_o$ and $p_l$ always positive) shows that $\eta$ must be less than 1.0.  T
We can also talk about efficiency of an energy storage device -- say a battery, flywheel, or spring.  Here again, we might use the symbol $\eta$, but we have to be extra careful.
First, we must make clear the energy we put in $e_i$, the energy stored $e_s$, and the energy we get out $e_o$.  When we put energy into a battery, we might think about a charge efficiency $\eta_c=e_s/e_i$.  When we draw energy from a battery, we might think about a discharge efficiency $\eta_d=e_o/e_s$.  Or, we might ignore the middle step and think about a round-trip efficiency $\eta_{rt}=e_o/e_i$.
This energy storage efficiency is not an instantaneous measure -- it takes time to charge or discharge a battery.  You might only partially charge (or discharge) a battery.
Energy is the integral of power over time $e=\int_{t_i}^{t_f}p\ dt$.  So energy storage efficiencies are integral measures of efficiency -- think of them as an averaging process.  As we charge a battery, any instantaneous transfer of power has some efficiency.  Over the complete charge, there is some average efficiency that reflects the energy (rather than the power).
This is just to say that we must be careful when working with efficiencies that we know exactly what definitions / conventions are being applied and what we can do with them.

Lift to Drag, (L/D), is just a ratio, so it is perfectly possible to be greater than 1.

That’s the whole point of an aeroplane really, to you allow to remain airborne with less thrust than your weight.

$η$ is also just a ratio, but it's impossible for it to be greater than 1. Maybe you can explain why that's not the case with L/D.

@AdityaSharma, a ratio can be any value. Efficiency is a matter of "how much of it is (not) lost during the process". That's why it starts from 1 (perfect) and ends with 0 (wasteful). However, a ratio [0,1], is an ordinary arithmetic division.

There's a bit of confusion here between a generic ratio and the ratio defining efficiency (or performance or figure of merit or whatever you want to the name it).

The ratio between two quantities is... well, the ratio between two quantities. If the forward chainring of a bike has 52 teeth and the chainring is engaged with a sprocket of 13 teeth, then their ratio is 1:4=0.25 (or 4:1=4). If I have five pens and my roof has 100 tiles, their ratio is 5:100=0.05 (or 100:5=20). If an airplane generates 4000N of lift and 500N of drag, their ratio is 4000:500=8.

Efficiency is the specific ratio of: (one quantity we are interested in) and (the whole). If 5 roof tiles are broken and 95 are good, the efficiency of my roof tiles is 95/100=0.95 (or the inefficiency is 5/100=0.05). The airplane of before generates a total aerodynamic force of $\sqrt{4000²+500²}=4031N$ and its efficiency in generating lift is therefore 4000/4031=0.992.
Note that being efficiency defined as (a part)/(the whole) then it is a number between 0 and 1. This implies that multiplying it by 100, we get efficiency in percentage.

We can move on, thanks.

@RobertDiGiovanni The point is not to just 'move on'.  You have have satisfied your understanding, but someone else who comes along later may have the same question and find this page -- or they might find it and become confused.  Please select a response as a correct answer to close out this question.  If no single response provided you with clarity, then answer your own question.  Once answered, we can all move on.

@RobMcDonald appreciate your response.  My question was more about a question where L/D was discussed.  I was simply clarifying L/D as a ratio of two quantities > 0, expressed as x : y, or a fraction of x/(x+y), but not anything that had a limit (mathematicly) or was generally used when one of the quantities was zero.  With our group efforts, I believe we can agree to L/D ratio of 100 is not an absolute limit.

But of course! Perhaps my view of this issue regards coming to terms with understanding the propeller thrust issue, and its relationship to the lift to drag ratio. Somebody asked 'what is performance ratio?'  Simply put, this is efficiency. How does one get 100 percent efficiency out of anything? The answer is only with great difficulty. But I digress...
With propeller thrust, we can do a lot of stuff. Going to the primordial equations, we find that if we know the power, velocity, and lift to drag ratio, we can determine the weight of the aircraft we can sustain in flight.  What's that, you may ask...
$$W = (L/D)*((lb \cdot ft/sec)/V)$$
Yes, interesting is how that equation resolves.  Now, as noted in the previously mentioned answer, we can re-define this equation algebraically to solve for anything else within the equation that we wish to know.  The only limitation is that we have to know the stuff on the right side of the equation. Specifically, the term in brackets, $(L/D)$, is the lift/drag ratio, is given properly in the equation by $C_L/C_D$.  We note, lb$\cdot$ft/sec is power, V is velocity in ft/sec.  The method for determining thrust has already been well sustained, elsewhere.  The performance ratio for the best propellers is about 88 to 89 percent.  In other words, the best propeller is about 88 to 89 percent efficient.  Consequently, propeller thrust is about 88 to 89 percent of rated power available to turn the propeller.  Assuming, of course, that the propeller is operating at its optimal speed and pitch relative to V.  An aircraft assessment invoking the above equation can be offered if necessary.

The "primordial equations".  Ah yes, those I am working on.  L/D.  Much better.  Thanks.

@RobertDiGiovanni  A small edit to provide proper perspective on the equation that was provided.  Note the addition.  The term in brackets, $(L/D)$ is given properly by $C_L/C_D$.  Both expressions, however, give the desired number, the lift/drag ratio.

L/D is a ratio of forces, so it can be greater than 1. A reduction gear also produces more output force (torque) than input torque. It does so by trading rotation speed for torque. That's precisely what an aerofoil does - the only difference being that it does so aerodynamically instead of mechanically.
$Power = Force \cdot distance/time$
An aerofoil trades Speed for Force (lift force), thus giving it an L/D ratio greater than 1.

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What does a pilot have to do in order to fly as a second in command in a private jet?
If a pilot has the opportunity to fly as an SIC in a private jet, what FAA requirements must they comply with in order to fly with passengers?

Don't know if the same rules still apply, but back in the 70s and 80s I used to fly legally as the second pilot on corporate jets with just a commercial license with IFR and multi-engine ratings. At the time I had no type ratings.

Theoretically you can fly a Boeing 747 on a Private Pilots Licence as long as you have the relevant type ratings. If you are flying passengers for profit you will then require at least a Commercial Pilots Licence.
Modern day training courses which prepare you to be the first officer or co-pilot as it were, tend to result in you holding a frozen ATPL, ie, you have done all the exams and you're now hour building in order to qualify for the licence. You will also likely have completed a Multi-Crew Co-operation course of some description, obtained your jet rating and hold any relevant Instrument Ratings. It probably depends on which provider you were choosing to apply for.
EDIT: Ah, my apologies, this post was in relation to European (EASA) guidelines (more specifically in the UK really).

If it were a privately operated 747 (which my question is about, not airline) then you don't even need a type rating do you?

In the UK at least, you would need to be converted onto type. Else you could just step from a Cessna 152 into a Boeing 747 after getting a jet rating, and obviously if you do not know how to fly the aircraft, you're in a bit of trouble! :D

In the US, no type rating is required for the SIC, however it is for the PIC.

In general, FAR Part 61, section 55a,b outlines specific requirements for those designated as Second-in-command of Aircraft requiring more than one pilot.  Section b probably covers the specific training you're curious about. See also parts 121, 125, and 135 for more specific requirements.

H brinky, welcome to Aviation StackOverflow!  When answering questions, we prefer that you include the pertinent wording from the sources that you quote, (and even a link to it if you have it handy!) so that the question is answered in one place.  Please click the edit link at the bottom of your answer to add more details if you want to improve it.  For more info, see [answer], thanks!

SIC: instrument rating, multi-engine (if more than one engine) Endorsements: high performance (200hp or greater)-high altitude - complex (retractable landing gear)

Jets are not “complex” because they don’t have a controllable-pitch prop.

@StephenS depends on jurisdiction. AFAIK under EASA anything with multiple engines and/or retracting gear is automatically complex.

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Under what conditions is a flight attendant required on an aircraft?
Not all airplanes with passengers are required to have flight attendants.
What are the regulations that cover this and when are they required?

14 CFR Part § 121.391.
It depends on the size/weight of the airplane and how many passengers it can hold

Except as specified in § 121.393 and § 121.394, each certificate
  holder must provide at least the following flight attendants on board
  each passenger-carrying airplane when passengers are on board:

For airplanes having a maximum payload capacity of more than 7,500 pounds
  and having a seating capacity of more than 9 but less than 51
  passengers—one flight attendant.
For airplanes having a maximum
  payload capacity of 7,500 pounds or less and having a seating capacity
  of more than 19 but less than 51 passengers—one flight attendant.
For airplanes having a seating capacity of more than 50 but less than
  101 passengers—two flight attendants.
For airplanes having a seating capacity of more than 100 passengers—two flight
  attendants plus one additional flight attendant for each unit (or part of a unit)
  of 50 passenger seats above a seating capacity of 100 passengers.

http://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol3/pdf/CFR-2011-title14-vol3-sec121-391.pdf
Parts § 121.393,394 relax these requirements when a plane stops, but denotes how close by the flight attendants must be, and other things like exit door requirements.
Remember, Flight Attendants are there for your safety :) which is the motivation for these regulations.
[Edit]
14 CFR Part 91.533 covers flights operated under "Part 91" regulations:
§ 91.533 Flight attendant requirements.

No person may operate an airplane unless at least the following number of flight attendants are on board the airplane:

For airplanes having more than 19 but less than 51 passengers on board, one flight attendant.
For airplanes having more than 50 but less than 101 passengers on board, two flight attendants.
For airplanes having more than 100 passengers on board, two flight attendants plus one additional flight attendant for each unit (or part
  of a unit) of 50 passengers above 100.

No person may serve as a flight attendant on an airplane when required by paragraph (a) of this section unless that person has
  demonstrated to the pilot in command familiarity with the necessary
  functions to be performed in an emergency or a situation requiring
  emergency evacuation and is capable of using the emergency equipment
  installed on that airplane.

It looks like the "training" to act as a Part 91 Flight Attendant is just showing the pilot they are capable.
The big difference between Part 121 and Part 91, is number of seats (potential capacity) vs. people actually on board.  This is interesting in light of the recent 787 Boeing Business Jet deliveries (http://boeing.mediaroom.com/2014-02-05-Boeing-Business-Jets-Delivers-First-Two-BBJ-787-8s-of-2014).  So if it was just the owner and the pilot crew, there wouldn't need to be a flight attendant (assuming, of course, they're operating under Part 91), even though it is a huge plane.

What about non-121 flights?

§ 91.533 covers this.  It seems like the Flight Attendant qualifications are little relaxed though. I'll update my answer.

Looks pretty good, is there anything special for 135, our is it the same as 91?

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text:
Is it legal to fly the localizer approach when cleared for the ILS?
Most ILS approaches include localizer minimums that can be used if the glideslope transmitter or receiver fails.  For example:

In this case, to fly the ILS you would intercept the glideslope just before PRAIZ and fly the 3 degree glideslope down to minimums.
If we were cleared for the ILS approach, but we instead wanted to ignore the glideslope and fly the LOC only approach1 (for whatever reason:  training, practice, etc.), could we do that without specific ATC approval since it is on the same chart and says "ILS or LOC"?

1 We could fly the LOC only approach by crossing PRAIZ at 2,200 ft. and then descend at an "optimum" rate until leveling off at the MDA of 520 ft.

What if you fly the ILS and you suddenly lose the GS? Do you (must you?) inform the tower or do you silently switch to the LOC only?

@Radu094 Yes, that is a required report per the AIM 5-3-3 - Additional Reports: "(h) Any loss, in controlled airspace, of VOR, TACAN, ADF, low frequency navigation receiver capability, GPS anomalies while using installed IFR-certified GPS/GNSS receivers, complete or partial loss of ILS receiver capability or impairment of air/ground communications capability...."

Related: ATC Approach Clearance Procedures: "Where more than one procedure is published on a single chart and a specific procedure is to be flown, amend the approach clearance to specify execution of the specific approach to be flown"

The question really boils down to: "ATC clears me to fly an approach.  Is the approach clearance defined by what is on the approach plate, or is it specific to the type of navigation equipment used?"  It turns out that it is based on the approach plate.
The answer is found here:
https://www.faa.gov/air_traffic/publications/atpubs/aim/aim0504.html
Section 5-4-5.a.3(a)

More than one navigational system separated by the word “or” indicates
  either type of equipment may be used to execute the final approach
  (e.g., VOR or GPS RWY 15).

When the chart is written as in your example, you are cleared for the approach, and you must use one of the approved types of navigational equipment to fly it.  There is no requirement in FAR/AIM to tell approach control which equipment you will be using (beyond the equipment code in your flight plan).
As further corroboration, section 5-4-7.d in the above document specifies that ATC is allowed to clear you for an approach even if the equipment required for some types of navigation systems is not available.  This actually is not that rare because NDB/GPS approaches are still used even if the NDB is not working.
The requirement to notify ATC in the event of navigation radio failure is separate.  Oddly, you don't have to tell ATC if you have a glideslope receiver at all, but you are supposed to tell them if one that you do have breaks.  If it happened while you were actually flying the approach, I would encourage you to execute a missed approach.  But if you just want to fly an ILS/LOC approach as localizer-only for practice, ATC doesn't care and you don't need to tell them.

While all of this is true, they don't clear you for the "ILS or Localizer Runway 8 Approach."  They clear you for the "ILS Runway 8 Approach" or the "Localizer Runway 8 Approach."

I disagree heartily with this answer. As Lnafziger said, ATC may clear you for either approach, but when they do you must fly the specific approach (either the ILS or the LOC) that you were cleared for. (Except at the end, where you say that ATC doesn't care... that probably is true, once you get inside the FAF at least. But it's still not legal.)

Practically, you could likely do it and ATC would not notice; however, you are not technically adhering to the ATC clearance as it was provided to you and as you read back.

§91.123   Compliance with ATC clearances and instructions.
(a) When an ATC clearance has been obtained, no pilot in command may
  deviate from that clearance unless an amended clearance is obtained,
  an emergency exists, or the deviation is in response to a traffic
  alert and collision avoidance system resolution advisory.

That's even very common when doing flight training, but instead of going to Exec I would sugest yo to shoot a real LOC (only) approach in Pompano just north of it ;)
I can't offer you the 100% legal, floorless, perfect answer for this but ther has been no trouble, yet. Probably the most correct option you have is to particularly ask for the LOC APCH for flight training, but if you demonstrate good airmen ship flying the approch, following a predetermined descend profile leveling off half a mile prior to your DTL, this sould even keep you within half scale until leveling off at yor MDA.
It doesn't matter on which plate the approach is printed, the key point for ATC is, that you are following the same lateral and approximately the same vertical profile, at pretty much the same speed. Ther is obviously no other technique to maintain seperation required.
Obviously you should not plan on doing this without one crew member having the runway inside, or at least with a cloud base reported well above your LOC minimums. If you fail your glide path indicator (put a sticker on it) and you are - for any reason - not visual with the runway at your minimums passing the DTL go around, do not change back to the ILS.


text:
Is it legal for a passenger to sit on the jump seat in Part 135 operations?
When operating a large turbine aircraft under 14 CFR 135, does the FAA allow a passenger to occupy the jump seat in the cockpit?

Falcon 900 jump seat
Would it matter whether or not they are a company employee (i.e. other than a flight crew member)?
Unlike the airlines, we usually fly with the cockpit door open (if there is even one installed) so it isn't a security issue like the airlines.

I'm wondering if an FAA inspector would deem the seat in the image to be a proper jump seat. I suspect some would say that a jumpseat should be facing forward to allow the inspector to view the instrument panel without having to turn their head. Just a thought.

A friend of mine who flies 737 once told me: "as long as you are a trusted individual by the whole cockpit, you can sit there". But that is just a quote and I don't think it will convince the FAA when something happens :)

@Jelmer Well, in an airplane like this there isn't even a door to the cockpit so it it's less of a security concern than in an airliner where access is limited.

Lets start with 14 CFR 135.125, which defines security requirements for part 135 flights:

§135.125   Aircraft security.
Certificate holders conducting operators conducting operations under this part must comply with the applicable security requirements in 49 CFR chapter XII.

We pass the ball to 49 CFR 1544 and make sure we're in the right place:

§1544.1   Applicability of this part.
(a) This part prescribes aviation security rules governing the following:
(1) The operations of aircraft operators holding operating certificates under 14 CFR part 119 for scheduled passenger operations, public charter passenger operations, private charter passenger operations; the operations of aircraft operators holding operating certificates under 14 CFR part 119 operating aircraft with a maximum certificated takeoff weight of 12,500 pounds or more; and other aircraft operators adopting and obtaining approval of an aircraft operator security program.
(b) As used in this part, “aircraft operator” means an aircraft operator subject to this part as described in §1544.101.

For brevity, I'm not posting 1544.101 which defines a host of paragraphs you must comply with depending on your operation.  If we assume a charter operation in an airplane weighing over 12,500 lbs, we get (1544.101(e)(1)):

(1) The requirements of §§1544.215, 1544.217, 1544.219, 1544.223, 1544.230, 1544.235, 1544.237, 1544.301(a) and (b), 1544.303, and 1544.305; and in addition, for all-cargo operations of §§1544.202, 1544.205(a), (b), (d), and (f).
(2) Other provisions of subparts C, D, and E that TSA has approved upon request.
(3) The remaining requirements of subparts C, D, and E when TSA notifies the aircraft operator in writing that a security threat exists concerning that operation.

From here the one we care about is 1544.237, which says:

§1544.237   Flight deck privileges.
(a) For each aircraft that has a door to the flight deck, each aircraft operator must restrict access to the flight deck as provided in its security program.
(b) This section does not restrict access for an FAA air carrier inspector, an authorized representative of the National Transportation Safety Board, or for an Agent of the United States Secret Service, under 14 CFR parts 121, 125, or 135. This section does not restrict access for a Federal Air Marshal under this part.

Which brings us to our answer: YES, a passenger may occupy the jumpseat if you do not have a door, and also if you do have a door as long as your company security program allows it.

Detailed answer but only applicable to aircraft with a door separating the cockpit from the cabin.  The aircraft in the photo, a Falcon 900 series, as is true with all Falcon 2000 and 900 series aircraft, is placarded as a part of the Certification of the aircraft, and all with jump-seats are placarded with a restriction that the seat can be occupied for takeoff and landing by crewmembers only. As each passenger must have an approved seat for takeoff and landing, this would preclude the assignment of the jumpseat for passengers.  In other words, if the aircraft is equipped with 10 passenger seats and the question is "can we use the jumpseat as a seat for the eleventh passenger, the answer would be no.


text:
Which FAA regulations cover the certification of aircraft engines?
Aircraft certification is covered by 14 CFR 23 and 25, what parts cover aircraft engines?

The relevant section of the FARs for engine certification standards is 14CFR33 - AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES, with 33.31 through 33.57 dealing with reciprocating (piston) powerplants & their testing requirements, and 33.61 through 33.99 being the equivalent for turbine powerplants.
There are also the 33 series Advisory Circulars dealing with such fun topics as how to comply with the Bird Ingestion Certification Standards (33.76-1A).


text:
What can I do as a bystander on the ground if I see an aircraft above me that appears to be failing?
If I'm watching an aircraft fly overhead and it becomes apparent to me that it is failing, what action can I take in response to this incident?
For now I will leave this question generic as to location, but if it becomes necessary to narrow it down I am interested in the US specifically.

Don't forget to bookmark the answers below, in case you see such case and can't remember what was suggested.

Honestly, very little.
First, be clear as to whether you are actually see something failing. If you see flames, or a wing has broken off, then yes, it's a problem. However, if you see someone doing a slow spiral towards an empty field with the power idling, they're more likely to be practicing engine out procedures (something that's required for all US pilots to practice and demonstrate during their checkride for their certificate).
In the event that you actually see an impact, fire, off-airport landing and so on, call 911 and give them your location. They'll send the appropriate crews.
Otherwise, if the aircraft is still flying, there's a strong chance the pilot(s) are already talking to ATC about their problem, if it actually exists. There's nothing you really can or need to do in this case.
Quick Anecdote: I've been told the story of a local police department who gets phone calls virtually every time a citizen lands his small airplane in his private field. Fire/police/medics/etc are summoned, when absolutely nothing bad has happened. This is why you should make an attempt to verify that a problem actually exists before reporting it.

Quite right.  Unless you see them on fire, a wing falling off, or actually crashing with parts breaking and fire and smoke, then don't do anything.  More than likely there isn't anything wrong.

Great answer! Hopefully, this will help people avoid calling 911 too soon.

Brian Tusi's answer is correct in that there's probably very little (most likely nothing) that you can do right then and there to help that particular aircraft, even if your assessment is correct in that they actually are having serious problems.
However, there is one thing you can do, and which has proven to be helpful in real-world accidents and incidents: document as much as you can, as quickly as possible.
Pull out your phone, or camera, or whatever else you might have handy that takes pictures or video. Set it to action mode if you have the time, but don't spend a lot of time fiddling with the settings. Pointing it at the aircraft, start photographing or recording video. If you're recording video with sound, say something about your location, the current time and maybe the direction you're looking in, in such a way that it gets recorded. (Especially cell phones will usually record your location in the image metadata; I'm not sure about video, but either way, it likely doesn't hurt to help.) If you're using a still-pictures camera such as a DSLR without video capability, you probably want to set the focus to manual and infinity, and then just keep snapping as many pictures as you can for as long as you're able to see the aircraft. Focusing at infinity will almost certainly be the right setting for anything at any distance where you're likely to be able to survive observing an aircraft accident without injury to yourself, and setting the focus to manual will keep the autofocus from changing the focus distance at an inopportunate moment.
I would advice against posting the video or pictures to any particular online service, for both social and technical reasons. Considering the needs of accident investigators should this be an actual aviation emergency, such services often recompress any video or images uploaded, which can lose detail, as especially video compression is almost always a lossy process. It's probably better to keep it as pristine as you can for the time being. Keeping the video to yourself also reduces the risk of influencing others, which besides possible impact on victims, their relatives and others, could potentially make investigators' jobs more difficult in trying to piece together what actually happened.
Once the immediate situation is over, you can contact your national aircraft accident investigation board, whatever they might be called locally. (NTSB in the US, AAIB in the UK, etc.) Ask them if there's an investigation ongoing for an event around the time when you saw something odd; if there is, offer to send them what you have, and work with them on how to deliver it to them. It's possible that they will want to interview you as well, as a witness.
If there is a bona-fide emergency going on, then those pictures and the details you might be able to provide in an interview just might provide accident investigators with just the clues that they need to figure out what happened. If there's not, then all you lost was a few minutes stopping and recording what was going on, and maybe a few minutes spent on looking up their phone number and making a phone call; after all, with digital photography, you can always just delete the pictures or video later.
As a final note, if you come across what you have good reason to believe is aircraft debris on the ground, don't touch it in any way; contact the local police. It's likely that they will want to get that to an aircraft accident investigation team; your contacting them may help them do so more quickly.

+1 for not blindly uploading on YouTube.  It might tempting, but this are humans in the planes. Making the video public can be reconsidered, when appropriate time has allowed thinking about it.

FYI, yes, videos can contain GPS metadata.

In addition to the suggestions in the other comments, you might do what this guy did, because your scenario just happened a few days ago:
Pilot praises RAF Lakenheath plane spotter for saving his life

A plane spotter who alerted an airbase to a jet "malfunction" averted a potential disaster, its pilot said.
Ian Simpson called RAF Lakenheath after seeing flames and sparks come out of Maj Grant Thompson's F-15E Strike Eagle on take-off.
Photographer Mr Simpson regularly watches jets take off from the United States Air Force base in Suffolk.
The pilot said Mr Simpson's quick actions had "100%" saved his life, adding: "His initiative was awesome."

Obviously it helps if you know where you are and what you're looking at, and in this case it seems as though it was fairly clear that there was a significant problem.


text:
NEXRAD—why is it 2D?
If you paid attention to NEXRAD training, you know that the colors of pixels show the maximum activity at any altitude in that air column. (It’s a “composite” view.)
NEXRAD itself samples in three dimensions, so that integration into the composite is being done on the ground before being sent back out on SiriusXM or ADS-B.
Given ADS-B’s bandwidth constraints, it makes sense that you only get maximums—it’s the thing that most pilots will care about. The bandwidth constraints are the same reason pixel granularity falls off with distance—the stations can’t send nationwide data in the bandwidth allotted.
But could SiriusXM give you the raw 3D data in addition to the composite view? They have the bandwidth where you could dial in a given altitude and get a 2D slice rather than just maximums. And you can get other data like wind on an altitude basis, so the capability seems to be there.
I don’t know if it’s a case of cost (considering how SiriusXM charges for subscriptions, I imagine they’d be happy to offer this to pilots as an additional tier), a worry that some pilots could take on even more risk around storms by trying to do 3D rather than just 2D daisy-clipping, or something else (like a technical issue with NEXRAD—as far as I can tell, none of the weather sites offering NEXRAD give the ability to dial in altitudes).
Given how many accident studies (even into incidents where the PIC’s were instrument-rated private pilots) have shown that pilots who flew into unexpected IMC or icing could have survived had they made a different decision about what altitude to seek for safety, it feels like it could be an improvement in situational awareness and safety, and usually we seem to accept those technologies in aviation, even if they may also present greater risk of recklessness.

An aircraft's shipboard weather radar can provide that 3D picture (by use of tilt and vertical modes). An aircraft's NEXRAD display is delayed with several minutes of latency and is typically used for big picture strategic planning. Shipboard weather radar is better used for tactical purposes.

One thinks that the pilots flying into unexpected IMC wouldn't be able to figure out how to use 3D data in a timely manner.  The risk is not about the altitude, but the lateral confines of the IMC and precipitation.  Additionally, clouds don't show up on radar, only precip does.  So NEXRAD won't help pilots avoid clouds.

Data about the height of precipitation would be useful in real-time avoidance of weather phenomena. In fact, this information is provided by NEXRAD and is known as "echo tops."  Echo tops also appear in suitably sophisticated SiriusXM weather displays.
However, ground based radar is not the primary tool used for weather avoidance, and in particular, datalink radar data, like Sirius XM should not be used for weather avoidance.  According to the FAA:

Unlike airborne weather avoidance radar, weather data linked from a ground weather surveillance radar system is not real-time information. The radar data displays recent rather than current weather conditions. As the current location of a thunderstorm cell may be different than the broadcast weather product, do not attempt to find a hole in a thunderstorm solely using data-linked weather. Pilots must avoid individual storms by visual sighting or by airborne weather radar.

Airborne weather radar does include three dimensional data.  The image here shows that a radar beam has height, as well as range and width.

In those cases where weather cannot be avoided completely, the pilot chooses the path with the least intensity precipitation.  This can include a climb to an area of lower intensity precipitation.
Finally, icing information, including pilot reports and forecasts is included in the SiriusXM aviation products, as detailed here. Thus one does not have to use NEXRAD height data and correlate to temperatures to avoid areas of icing.

Your answer addressed the question as asked, so thank you for that. This question occurred to me frequently in reviewing accident reports when I noticed that icing and other Wx issues where the same flight path at different altitudes would have resulted in radically different outcomes also seemed to be excruciatingly long in duration, compared to most accident report emergencies—sometimes many hours between recognition of issue and point of no return. So there was time to consider things like condition stratification; but would the tech to do so have helped? Thanks for the answer.

There is not much gained by the third dimension for your use case. In GA you generally want to avoid any active weather. Why make it more complicated?

can't go over it (performance limited)
can't go under it (microbursts can kill you)

=> only way is to go around it and therefore no need for that 3D information.

Chris, I may have made a big mistake by mentioning “GA” in the question—the only reason I did was because there hasn’t been a weather-related airliner fatality in the US in so long that the recent incident reports are all GA. But many involved aircraft—e.g. (video) in a Socata TBM-700—aren’t so performance-limited as to make altitude information completely useless.

@Trey, you linked an icing-related accident, but radar does not provide any information about icing. It only provides information about precipitation and convective activity (storms).

@JanHudec sure—but you can get freezing level with ADS-B or SiriusXM, and the formula there is pretty straightforward: above freezing level and in precip, icing. Climbing out of precip will avoid icing, even if aircraft below you might be icing. There have been three incidents since 2000 just in those that AOPA’s Flight Safety Institute has reviewed where climbing above precip rather than trying to descend below freezing level would have been better.

Correction: I mean’t “climbing above precip”, not “climbing out of precip”. Obviously if you’re already getting ice accumulation, you have to get below freezing level to get rid of it (if you don’t have a de-icing system). But climbing to where you never get ice in the first place can do the job, too.

@Trey, no, it's not that simple. The radar sees both water droplets (where you get icing) and ice crystals (where you don't), but only if they are large enough and only if they are affected by some turbulence. Rain not associated with convective activity shows weakly or sometimes even not at all, but is more likely to cause severe icing as the water droplets are staying at their level while convective activity would bring them higher where they'd freeze.

The danger of VFR flight into IMC is flying into clouds when you aren't properly trained for it. Icing generally only occurs in clouds between -20°C and +5°C.  NEXRAD shows the strength of the radar returns, which is usually an indicator of precipitation intensity, though, not clouds, so it doesn't really help avoid either of those things.
Regarding why NEXRAD isn't 3D, precipitation almost always falls to the surface, so there is no need for a minimum altitude. On the other hand, taller storms tend to be more intense, so you have a good idea what the maximum altitude is just by looking at the color. Generally speaking, if precipitation is too intense to fly through in a particular plane, it's probably too tall for that plane to climb over as well. So, there's no practical benefit to 3D.

In more severe storms, much of the precipitation does not fall to the surface initially, but is carried about with up and down drafts. This is an important consideration when looking for possible areas of hail (for the pilot this is typically done with onboard radar, though 2d radar like NEXRAD can also be informative).

I would question your comment about the precipitation intensity related to the height of the storm. The aircraft that I fly can fly at FL450, and top many medium intensity thunderstorms. I have flown over large, severe storm systems that have brought tornados and caused deaths on the ground. Flying through many parts of these storms could have been deadly, but flying overtop the storm was smooth and uneventful.

StephenS—again, like in my response to the other answer, I may have injected too many assumptions by mentioning “GA”. In this case, I didn’t necessarily mean non-instrument-rated pilots entering IMC or icing. Unexpectedly entering IMC with moderate-to-severe Wx can be a problem even for instrumented-rated pilots (though pretty much exclusively GA pilots, since their IMC flight hours logged will be much lower). A pilot flying e.g. @JWalters FL450-capable aircraft (including jets!) may, in fact, be GA—even though that’s not at all what we imagine when we hear “GA”.

@JWalters FL450 is exceptionally high, possible for maybe 1% of GA traffic. And by the time someone is flying such planes, they should have the experience to not fly into danger despite a lack of 3D NEXRAD. The other 99% will be flying around any purples, reds and maybe yellows rather than trying (and probably failing) to fly over them.

Ok, we must be working from different definitions of GA. I have only ever flown GA by some definitions, even under §135, but flying a light jet under §91 would generally be included under GA. Let me assure you that there are a great many §91 jets and turboprops that can top storms that the pilots would otherwise not fly through.

I obviously erred in mentioning GA. I’ve edited the last paragraph of my question, to “Given how many accident studies (even into incidents where the PIC’s were instrument-rated private pilots) have shown that pilots who flew into unexpected IMC or icing…”. Maybe that will clarify that I wasn’t asking about why Skyhawks don’t have greater altitudinal striation in weather tools, for which the answer “because they don’t need it” makes perfect sense.

@JWalters, but are you relying on NEXRAD or do you have an onboard weather radar?

@JanHudec That depends which aircraft I am flying. I fly several with NEXRAD, and one without. All have onboard radar as required by regulation. NEXRAD is best for strategic planning, and onboard radar is good for tactical avoidance. Neither will detect many turbulent buildups that can only be detected visually, if at all.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How much is a swashplate system more energy efficient than a fixed blade system for the same load
When reading about the lifting capacity of swashplates (as found in helicopters) vs fixed blade systems (as found in e.g. DJI drones), I read a lot of comments about the fact that the bigger rotors of a helicopter are more efficient. But how does that link to the system (fixed vs swashplate) and how much efficiency are we talking about? Now, I know that the question is way too simple for the complexity of the problem, also after reading these questions 1, 2, 3
The factors that influence this problem is also part of the 'quest' and I hope to reach a ballpark figure. It also links to the complexity of the use of a swashplate or even a virtual one. A very complex system can be more efficient in the long run, but is it worth it. That is the underlying question.
If possible could you explain formula's? I had math and physics back in the day until the age of 18 (VWO for the dutchies), so it is rather rusty.
edit: the core of the question is the system efficiency vs 1 or multirotor

This ain't that easy to answer, as aerodynamics do not scale in a simple manner. Drones and helos are soooo different in size, and there is huge variation in their niches... Way outside my comfort zone ;)

Not to mention that drones and (non-drone) rotorcraft come in quite a range of sizes (likely overlapping - if not now, then certainly quite soon).

A helicopter is generally massively more efficient than a multirotor, in part because of the rotor diameter and in part because of the fuselage's wetted area. BTW, drones are anything which fly autonomously, so there are drone helicopters as well.

Drone is a misleading word here.  You could turn a large helicopter into a drone, just by adding some actuators & electronics so that it could be controlled by a remote operator instead of a pilot.  E.g. https://www.popsci.com/technology/article/2013-04/full-size-helicopter-actually-drone/

The (first) edit was an improvement (removing the word "drone") -- but arguably it invalidated an existing answer-- it seems the most correct course of action would be to roll back and allow original asker to post a new question if he/she wishes-- but maybe the answerer doesn't mind in this case-- ??  We can still upvote the answer after all even if it no longer fits the present version of the question; it should be pretty obvious to everyone that it suited the question as it stood at the time it was posted--

Thanks @quietflyer, I rolled back and clarified that my concern is the system, not the amount of rotors. And I removed the word drone which turned out to be confusing.

The question is inconsistent. Fixed vs. swashplate and single vs. multiple rotors are independent properties.

Swashplate compared to fixed-blade system
Makes no difference. The swashplate is there for controlability, not efficiency.
Of course single-rotor fixed-blade system can't be used, because it wouldn't be controllable, and with four or more rotors nobody uses swashplate, because it is controllable without it, but that's orthogonal to efficiency.
Single-rotor compared to multi-rotor
The efficiency depends on area for weight and RPM. Increasing the area reduces the induced power (energy carried away by the slipstream), but it also increases the parasite power (energy needed to overcome parasite drag of the larger, faster moving blades), so there is some optimal size for given lift.
Now the thing is that as weight increases, the optimal area increases slightly slower, and the best possible efficiency decreases. From this it follows that four rotors of quarter the lift each are more efficient than one big rotor.
This is however offset by the weight of the structure and transmission needed to use four rotors, and by larger turbine engines being more efficient. That, plus all the safety benefits of a swashplate system is why single-rotor helicopters are more efficient in practice.
For small sizes the optimization criteria. Due to the square-cube law small scale UAVs have plenty of power for their need, so the efficiency is not that important, the materials are plenty strong for the need, and the simplicity of fixed blades driven by four separate electric engines is the main reason to choose multi-rotor setup.
Other reasons for swashplate

Swashplate systems are capable of efficient auto-rotation, so even in case of an engine failure, a helicopter can still glide to a safe(ish) landing. This requires reducing the blade pitch, so fixed-blade systems can't do it.
Swashplate can compensate for the different amount of lift on the advancing and retreating side by adjusting the blade pitch, so it copes better with high flight speeds.
Larger rotors have significantly larger moment of inertia (moment of inertia grows with fifth power of diameter!), so their RPM can't change quickly enough to give practical control response and variable blade pitch is needed to control their lift instead.
Multi-rotor with separate engine for each rotor have a problem dealing with engine failures. If an engine fails, they have to reduce power on the opposite side by the same margin and still not only have enough power to stay aloft, but also enough spinning rotors to stay controllable. That's why the Volocopter has so many rotors (rather than just four).
Electric propulsion does not provide the power-to-weight ratio needed for large helicopters, but separate electric motors is what makes multi-rotors simple.

If I understand it correctly you write that controllability is orthogonal to efficiency. I do not really understand 'orthogonal' in the sentence, would you mind to elaborate?

‘orthogonal’ in this sense means independent. You pick some parameters for sake of one and it does not have much effect of what parameters you need to pick for the other.

The question does not really make sense: a helicopter is a kind of aircraft, a drone is a mode of how a vehicle is controlled.
I can rip the seats and controls out of a helicopter and put some clever software, some cameras, and some transmitters inside, and boom: I have a drone that can carry exactly as much as it could before – probably even more because humans and safety systems are heavy, and we got rid of both of those.
In fact, that's exactly what some companies are doing. The Northrop-Grumman MQ-8C Fire Scout is literally just a Bell 407 with some added electronics and software. And while this particular drone is designed for combat, there are others which are designed for cargo delivery. For example, two uncrewed Kaman K-MAX were deployed to Afghanistan already in 2011.
Here is a video about the Office of Naval Research's Autonomous Aerial Cargo/Utility System AACUS program. The goal of this program is to have a software/hardware package that can be installed in any helicopter to make it fully autonomous. There is no reason you couldn't install it in a Mil Mi-26, for example.
So, in short: by turning an existing helicopter into a drone, a drone can by definition lift just as much as a helicopter. By designing a helicopter specifically as a drone, you could potentially lift even more, because you can get rid of all the weight for the cockpit, seats, life support, safety systems, controls, etc. You could also remove a lot of redundancy, if you consider occasional crashes acceptable when no humans are on board.


text:
How close do you have to be to an underwater black box to detect it?
The news keeps talking about the black boxes on aircraft that end up in water, and one thing that keeps coming up is the underwater locator beacon that transmits a signal for 30 days if it gets wet.
What kind of signal does it transmit and what kind of range does it have?  I'm guessing that the depth of water that it is in will affect how far away that it can be detected, but by how much?

This excellent explanation is taken from Avionics News in 2006:

FDRs are equipped with an Underwater Locator Beacon (ULB). If you look at a picture of an FDR, you will almost always see a small, cylindrical object attached to one end of the device.

If a plane crashes into the water, this beacon sends out an ultrasonic pulse that cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment.
There is a submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the beacon.
The beacon sends out pulses at 37.5 kilohertz (kHz) and can transmit sound as deep as 14,000 feet (4,267 m). Once the beacon begins "pinging", it pings once per second for 30 days.

Newer FDRs can now transmit as deep as 20,000 ft.
The following table is taken from a fascinatingly detailed article on Hydro International about the retrieval of black boxes. It shows the radius you can pick up the signal of a pinger from:

Notice that if pingers were replaced with more powerful transponders, the range could be drastically improved!
The article also points out, that in very deep water:

under normal conditions, the existing pinger would not be detectable from the surface in depths exceeding 2km

I imagine that the performance characteristics of their underwater passive sonar is something that most Navies are not inclined to discuss openly.  In deep water it will also be highly dependent on background noise, halo and thermo-clines the topography etc

I wonder if the pinger could send one pulse per second for 15 days, one every two seconds for another 15 days, then one every four for 15 days, one every eight for 15, etc., or if factors other than energy capacity are responsible for the 30-day limit?

You says it shows the "radius" in which we can pick up the signal, but then the figure states it's the max "depth"...
So is it the radius at the surface of the water, or the depth distance below the surface ??

3km..just one mile away from the source. They must be right over it, if they heard the ping for  2 hours 20 minutes. But the Chinese guys with the more primitive gear...what were they hearing...maybe the other recorder.

The Haixun 01 and the Ocean Shield are 300 nautical miles apart so it's hard to see how the signals they each detected could be from CVR & FDR from the same aircraft. Also The Ocean Shield is reported to have detected two independent signals in the same vicinity.

Sound waves travel through water for incredible distances. For example world war two mines were still to be heard many hundreds of miles from the original source of the explosion and more interesting, they were heard several years after the event that caused the sound wave, so it is probable that it was the sound waves of pings rather than the actual ping that has been detected.

I think it does -- per the table in Danny Beckett's answer you have a maximum of 7km range. If the black box is 4km deep in the water, you would have to be no more than 3km from it to hear it.

If you're 4 km up and 3 km to the side, that's only 5 km straight-line distance. With your numbers the surface distance would be more like 5¾ km.

Per the table, a pinger is only detectable within a max range of 5km in good conditions.


text:
What is the difference between a POH and an AFM?
Some aircraft come with a Pilot Operating Handbook and some come with an Aircraft Flight Manual.  Why the different name, and is there a difference between them?

Both a POH and an AFM meet the "Operating Limitations" requirement in the ARROW acronym.
The difference between the two is mainly in length and content: an AFM is usually a thinner document, satisfying the requirements of FAR 23.2620 and not much else, while a POH contains these required items plus other information like system diagrams (The contents & format of a POH are standardized in GAMA's Specification 1).
Parts of the POH (like the Limitations section) are FAA-Approved, and serve as the AFM, and both documents are typically associated with a specific airframe (by serial number).
A better explanation might be this:
The AFM is a regulatory document (it's contents are prescribed under the section of the regulations the aircraft was certificated under - Part 23, Part 25, etc). The POH is a GAMA-defined document whose contents meet the regulatory requirements of an AFM, and present other information in a standardized way so that a pilot can go from a Cessna to a Piper to a Mooney to a Socata and browse the book to learn about the airplane they're about to fly with all the information presented the same way no matter who the manufacturer is.

The other two types of documents you may encounter are an "Owner's Manual" (which usually goes along with a thinner AFM & provides some of the information found in the newer-style POH) and a Pilot Information Manual (PIM) which is a "generic" version of the POH which many pilots buy so they can study the procedures without removing the regulatory document from the aircraft.
Chapter 9 of the Pilot's Handbook of Aeronautical Knowledge talks a little about the differences between the two documents (and a whole lot of other flight documents).

I'd like to add that an AFM is not required for aircraft manufactured before a certain date (1975?). However a POH is still required to be in the plane. After that date, an up-to-date AFM with information for that specific airframe is required. Sometimes AFMs will be short, with just the airframe-specific information, and sometimes they will be the entire POH re-written.

Ummm, I don't think that this is quite right.  The AFM (not POH) on my Falcon is 7 volumes, all of which are 2" binders.....

@Lnafziger Does your Falcon fall under pt 135 or 125? They greatly expand the requirements of the AFM. Often it will combine the certificate holder's operating manual. Also, I must amend my previous comment that a POH is NOT required, but some form of compliance to 91.103 must be, and a POH satisfies that.

@StallSpin No, the AFM is from the manufacturer and comes with the airplane (who had no idea what operating rules will apply).  I fly two Falcon 50's. One is operated under part 135 and the other under Part 91. They both came with almost the same AFM (differences being serial number specific).

@Lnafziger 125.75 allows operators to carry a combined manual, and modify the AFM to suit their certification. I thought I read something similar for 135 but I can't find it now. Anyway, I don't know what to tell you other than that the Falcon is a very complicated airplane. It may be filled with a lot of non-approved sections? The POHs for both the light aircraft I fly are almost twice as thick as their AFM counterparts. Their AFMs have only the required approved sections in a binder and that's it, like voretaq7 said.

@StallSpin Well, it's probably possible to create a combined manual, but in reality 135 operators have a different FOM/GOM which has nothing to do with the specific aircraft type.  The manufacturer on all of the jets that I have flown (various Learjets and Falcons) all provide an AFM and none of them have a POH.  Hence, the question.

@Lnafziger The Falcon actually falls under Part 25, which has a slightly more substantial AFM requirement (beginning at 25.1581) -- I would also assume that a few of those volumes are also material that would show up in a Part 23 aircraft's POH (which may be informational or "FAA Accepted", but not necessarily "FAA Approved"). Pages that are FAA approved meeting the AFM requirements in the regs should be "clearly marked" (or specific sections may be noted as FAA approved).

(Posting as an answer because formatting.  Quoting from the spec directly, as an FYI which some may find interesting.)
From the GAMA standard for POHs (GAMA Specification 1, rev 1996), section 0.7:

The title [of the document shall be] "Pilot's Operating Handbook
and FAA Approved Airplane Flight Manual" for all airplanes except
those for which the airplane manufacturer elected to provide a
separate FAA Approved Airplane Flight Manual. In the latter case, the
title shall be "Pilot's Operating Handbook".
Note: After the effective date of this revision, Pilot's Operating
Handbooks for newly manufactured airplanes must be FAA Approved
Airplane Flight Manuals.

Also of interest, since it speaks to intention, in the Preface it says,

This Specification is designed to provide guidance for the preparation
of Handbooks for all types of general aviation airplanes originally
certificated at maximum takeoff weights of 12,500 pounds or less

The Specification contains little, if any, new material or novel
approaches. Basically, it is a guide to industry standardization of
proven concepts to be presented in a form most useful to pilots.
The Federal Aviation Administration has reviewed this Specification
and has ". . . determined that a handbook that would meet the
specification would also meet the intent of the requirements in FAR
23, which is to provide the pilot with all of the information needed
to operate his aircraft in a safe manner." The Federal Aviation
Administration recognized that compliance with this Specification will
result in a high degree of standardization of content and format for
all aircraft types and this will lead to a level of safety equal to or
higher than is required under FAR 23.

While both POH and AFM are generally used to mean the same thing, they do have some specific differences.
AFM is meant and built specific to make and model, or by serial number. In fact, while other aircraft of the same make/model can have very similar AFMs, they are usually tailored for that specific aircraft.
Not only is it FAA/regulatory approved, it contains specific instructions that pilots comply to operate the aircraft safely.
POH is contains similar FAA/regulatory approved information, and should indicate certain sections of the documents are approved. For the same make and model, they generally use and refer to the same POH. Mostly used in General Aviation, the POH is also known as the standardized AFM, following the same exact format.
I'm currently training to be a CFI, and this is a pretty tough question I have to prepare to answer my students.

All the above answers are wrong. A POH is a 'kind' of AFM. All aircraft must have an approved AFM. Before 1978 this could be anything (owners manual, POH, etc.). After 1978 GAMA (General Aviation Manufacturers Association) decided to standardize the AFM around the POH format. The name POH stuck… but it is still a kind of AFM.

Welcome to aviation.se! do you have any source to back up what you say?

All you need to know is that an AFM is specific to an aircraft serial number. A POH is less specific and generalized for a particular make or model

The POH is the official book of rules for that specific serial number airplane.  The AFM is the unofficial/generic one for a type of airplane that may or may not match the one it's in.  On occasion you'll run into a book labeled "AFM" that is in fact actually the "POH" (often due to an STC requirement).

You're thinking of a "PIM" (Pilot Information Manual) or "Owner's Handbook". An AFM is serialized & associated with a specific airframe.


text:
Can a US pilot fly a foreign registered aircraft in the US?
Is it legal for a pilot with an FAA license to fly a foreign registered aircraft within the United States?  Is it covered by FAA regulations, or the country of aircraft registration?

Yes. 14 CFR 61.3(b) covers this (my emphasis):

(b) Required pilot certificate for operating a foreign-registered
  aircraft within the United States. No person may serve as a required
  pilot flight crewmember of a civil aircraft of foreign registry within
  the United States, unless—
(1) That person's pilot certificate or document issued under §61.29(e)
  is in that person's physical possession or readily accessible in the
  aircraft when exercising the privileges of that pilot certificate; and
(2) Has been issued in accordance with this part, or has been issued
  or validated by the country in which the aircraft is registered.

So a US license (i.e. one issued under part 61) is allowed as an alternative to a foreign license for operating the foreign aircraft. The other country could have rules on this too, but I have no idea if they would be enforceable (obviously, one country's laws are usually not valid in another one).

The rules probably may not be be enforceable against the pilot, but they may be enforced against the owner or operator who are likely resident in the country of registration.

There are reciprocity treaties requiring most countries to allow foreign aircraft to fly in their airspace. It probably depends on whether the country involved has such a treaty in place with the United States.
See bilateral treaties and AOPA importing requirements.
In general, the FAA tolerates foreign aircraft to be operated in the US indefinitely so long as they meet airworthiness standards. In theory, they claim you have "imported" the aircraft and require you to re-register it, but this does not normally happen.

Hi Tyler, my question isn't about foreign aircraft operating in the US, but rather whether a US pilot can operate a foreign aircraft in the US.

Of course. Many foreign airlines employ US pilots to fly their planes all over the world, including the United States, and private planes and charters are no different.

Validate? I don't know how to make this any clearer. A pilot with either a US license or license from a country with which the US has a bilateral agreement can fly any plane for which they are qualified in any country and it does not matter whether the plane is registered in that country or not.

@Lnafziger Thats foreign governments, not the United States. You asked about the United States.

@Lnafziger A foreign government cannot dictate who or who may not fly their planes in the United States. If I have a friend with a plane registered in Germany located at an American airfield, the friend can allow me to fly the plane and there is nothing the government of Germany has to say about it. What are they going to do, say "we found out you let an American pilot fly that German plane so we are revoking its registration" ??? Where are you going with this line of questioning? I don't understand what you are getting at.

Okay, my main question that is left unanswered is the end of my previous comment.  Do you have any references to support your point of view, or is it just your opinion?

@Lnafziger It is my opinion from general knowledge as pilot. Of course, how do you "prove" that a law does not exist? You are apparently imagining some fabulous and mysterious regulation by some unnamed foreign country that somehow would legally control what planes I fly. I cannot prove such supposed regulations do not exist, but I can tell you I certainly have never had anyone try to interrogate me about my right to fly a plane based on its country of registration. Moreover, I can tell you bilateral treaties are pretty lenient about what they allow.

Okay, thank you for your answer.

FYI, I'm going to delete my comments that are not related to the actual question/answer.  You may want to do the same to keep it from looking like a one-sided conversation and to keep the site tidy.  :-)  You may also [edit] your answer to add anything that you said in a comment so that the comment may be removed.


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What G forces does a pilot perceive in a "1 G" barrel roll?
This is a follow on to an earlier discussion about pilot perception of G forces compared with actual aerodynamic loads on an airframe.  Years ago, the Boeing 707 prototype famously did not one, but two 1G barrel rolls to impress potential buyers. I would imagine the expert pilot just kept the airframe at 1G positive load through the entire maneuver, which would put him weightless at the top of the roll (plane inverted).  Is this what actually happened?  How is this done?

He was not weightless at the top of the roll, he experienced 1G... Bob Hoover famously demonstrated this by pouring a glass of water while barrel rolling, the G force remained constant throughout the roll. I think you are trying to add the 1G aerodynamic load to the -1G of gravity to get to zero, but the force felt throughout the entire roll is 1G relative to the outside of the loop.

@RonBeyer  Bob Hoover pours iced tea while doing a barrel roll in this video.

The title could use some improvement.  Do you really want to give the answer to the question in the title?  PS is there any such thing as a 1G barrel roll meaning 1G from start of initiation to very end?  Seems unlikely.

@quietflyer The title seems fine to me: what G forces does the pilot perceive when the aircraft is subject to 1G of aerodynamic forces?

G force on G-meter is same as G-force that pilot perceives, which is same as the G-load exerted on the aircraft structure.  It's all the same.

The only thing NOT the same as all of the above is the ACTUAL acceleration of the aircraft through space which offset -1G from the felt acceleration.  Two quick examples-- straight and level flight -- "felt" acceleration 1G, actual acceleration 0G.  "Zero G" ballistic flight-- "felt" acceleration 0G, actual acceleration 1G downward (i.e. -1G).

@ Tanner Swett PS if the title had been exactly as you stated than I would not have raised an objection.

You can't do a barrel roll at 1G.  It's a loop pulled out into a coil, and you have to pull pitch to get it started so you are going to be 1.5 to 2 starting out, declining to 1G to .5 at the top, and pulling 1.5 to 2 on the pullout.
So the sensation at the start is like a hard climbing turn (which is what you're doing), pressed into your seat with about the force of a steep turn at the start, declining to normal gravity or bit less (giving a bit of that giddy becoming weightless sensation, but not coming out of your seat) as you ease off the pitch coming around the top, and about the same pressed into the seat force as at the start, or a little more, on the pullout.
A good barrel roll should be no more than 2Gs peak, but how much is a function of pilot skill and of the airplane's ability to keep up the energy through the first half.  A jet with oodles of power to keep the speed up in the steep rolling climb can get away with a very gentle pull and will see only about 1.5 or less on the pull up and pull out.
But it's always going to be more than 1 starting out and finishing off and when Tex Johnston said in an interview it was a "1G maneuver", he really meant "not much more than" as in less than 2 (and no worse than a steep turn, unless you screw it up and fall out).  Watch the film of the barrel roll and you see a firm pull up at the start with a fairly steep nose down attitude on the exit, which would have required a pull of at least 1.5 G in returning to level flight without over speeding.

Outstanding answer John.  So the airframe is always positively loaded around 1.5 - 2 G, with pilot "feeling" 0.5 - 1 G at the top (being head down).  Perfect, thank you so much.  Now I'll work on the control inputs.

It's a weird sensation at the top of the roll, because "down" is blue sky, and "up" is green earth. Loops are similar, but the pull force and G load at the start and end is much higher because all the energy is directed in the vertical plane.  A loop will be 3 Gs during the initial pull and 1G or less over the top.

Ah, interesting, I didn't know the "1 G " reference came from an actual interview with the pilot.

So you all see where we are going with this, using aerodynamic load to compensate for negative gravity over the top (inverted) flight, either with elevator, thrust, or both.  I was fooled by the terminology "barrel roll".  It is a pitch and roll (now able to make Gs with el).  Bob Hoover was a genius.

@qqjkztd A jet like that with a thrust to weight >1 can "roll" at any G level it wants.  It can do it while in a ballistic arc, which can be sustained for 30 sec or more, and be 0 G through the entire roll.  That's not a barrel roll though, which is a centrifugal force maneuver.

Ballistic arc such as orbit, no?  Great stuff!  Thanks.

That's how they train astronauts.  A KC135 with the padded interior dives, pulls up into about a 30 deg climbs, pushes until G load is 0, and sustains that until the nose is pitched down in a dive, then pulls out.  2 Gs at the start and finish, with about 30 seconds of 0 G during the arc.  I can do it in my own plane but at 130 mph I can only sustain the 0 G state for about 3 seconds at the most, plus the engine quits momentarily and all the crap and dirt in the cockpit comes up and floats around your head.

By common terminology, when we speak of an "X G manuever" (say X=1 so a "1 G maneuver"), we mean that 1 G is the up-and-down acceleration indicated on the G-meter on the panel, and it also is the up-and-down acceleration (force per unit mass) acting to create stresses or strains on the aircraft's structure (and the pilot's body.)  In other words, it is the "felt" acceleration or force per unit mass, or at least the up-and-down component thereof, in the pilot's reference frame.  To get the ACTUAL up-and-down acceleration component (or force per unit mass) in the reference frame of the aircraft and pilot, we need to subtract the 1 G acceleration of gravity, or more precisely, the component of the the 1 G acceleration of gravity that acts in the up-and-down reference frame of the aircraft and pilot.  Why?  Because gravity exerts an equal acceleration (force per unit mass) on every molecule of the aircraft and pilot simultaneously and thus creates no stresses or strains within either, nor does it tend to accelerate the pilot toward or away from the aircraft and seat, so it is not a "felt" acceleration.
Two examples-- straight and level flight -- "felt" acceleration 1G, actual acceleration 0G. "Zero G" ballistic flight-- "felt" acceleration 0G, actual acceleration 1G downward (i.e. -1G).
So, in any maneuver that would commonly be described as a "1 G" maneuver, the G-force perceived by the pilot is +1 G, by definition.
Can a barrel roll be a "1 G" maneuver in this sense?  Sure, as the aircraft goes over the very top of the roll.  Can it be a "1G" maneuver in this sense from start to finish, including the initial pull-up and final round-out back to level flight?  No it cannot.  The barrel roll involves an arcing trajectory, and the G-load must be greater than 1-G during the initial pull-up and final round-out.
By the way, the "felt" acceleration as described above, is nothing more or less than the net aerodynamic force generated by the aircraft in whatever axis we are speaking of, or in all three axes if we want to be comprehensive.  Normally we are most interested in the forces acting in the up-down direction in the aircraft's reference frame-- that's what the G-meter on the panel indicates-- and this is overwhelmingly dominated by the lift force generated by the wings.   So when we speak of "feeling" 1 G (or "perceiving" 1 G), we are just saying that the wings are generating a net force equal to the mass of the (aircraft + contents) times the gravitational acceleration constant times two.
It may be sometimes a bit ambiguous as to whether the term "G-load" is being used to refer the TOTAL "felt" acceleration, or just the component that acts in the upward / downward direction in the pilot's reference frame.  Either way, if we label a maneuver a "1 G maneuver", the logical conclusion is the the pilot is perceiving a 1-G acceleration-- i.e. the aircraft is exerting a 1 G force (per unit mass) on the pilot.  Just as in straight and level flight.

meant to comment in another place.


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Could the center of rotation of a spinning aircraft move away from CG?
Picture a barbell shape or twirlers baton spinning.  Perfectly symmetrical.  Rotating at its center of gravity.
Now replace one of the ends with fins of equal mass an spin it again, once in a vacuum, then in air.  Will the centers of rotation be different?  Why?  Could this apply to aircraft?   Thanks.

In a spinning aircraft, is the axis of rotation even within the aircraft? I would have thought it would be way outside the aircraft.

What, exactly, do you mean by "center of rotation"? You need to edit your question to explain what you mean by "center of rotation", because clearly you are thinking it means something different from what I think it means. I'm flagging this question as unclear, because until that's explained, the question isn't sufficiently meaningful to be answered.

Actually in a normal erect spin the center of rotation is offset from the CG slightly.

In what reference frame?

In some sense, rotation is rarely around the centre of mass. It is extremely convenient to consider any motion as rotation around CM plus translation of that CM, but it doesn't have to be so.
Take the most basic control input for example: from level flight, you pull up for a short climb. A typical explanation of what happens says that the tail produces a pitch-up moment, which rotates the airplane around its CM to a higher angle of attack, this increases lift and it starts to climb. However, a more detailed analysis will point to the fact that initially, the tail will produce an extra negative lift. This is not just a pure moment, this is an unbalanced force applied away from CM. As a result, the airplane will lose some of its lift and will start sinking. Only later will lift grow and pull the airplane up.
Now, if you consider it as a single motion (which it is, fundamentally), you can rightfully say that it is a pure rotation about a point ahead of CM. (It would be nice to draw a diagram here, but not now). The pilot will perceive it as such. On some designs, particularly with delta wings, this initial loss of lift from elevons is so strong that the virtual point of rotation can be ahead of the aircraft (and thus the cockpit). Space shuttle reportedly had such configuration. For pilots, this creates a weird sensation that the aircraft behaves contrary to the expectation, particularly on landing where perception of altitude is acute. This can lead to pilot-induced oscillations.
So, for any motion, not only spin, to say that rotation always happens around CM is a simplification. To be able to say that and remain valid, you have to consider all the translation effects as well. In most cases, this is still the easiest way, but if you want to speak of rotation alone, remember that the instantaneous centre of rotation rarely aligns with CM.

The downforce of the elevator that you speak of here is quite pronounces on long airplanes like the A340. If you don't flare early enough you can pull all you want, the aircraft is not going to pitch up but rather be accelerated down by the elevator downforce.
Same happens on the vertical axis, too. If you apply full rudder the aircraft almost rotates about the cockpit, not around the cm. I love watching that on crosswind landings, the cockpit stays on centerline whilst the rest of the aircraft, including the CM moves left and right :D

@Jan, the force is even more pronounced on short airplanes. By definition, if you have a shorter arm, you need greater force for the same effect. This is why delta wings are so prominent in this regard.

In some sense, rotation is always around centre of mass: an unbalanced force causes linear acceleration of centre of gravity and a torque (moment of force) causes angular acceleration (rotation) around centre of mass. This decomposition follows simply from laws of conservation of linear and angular momentum.
However a spin is a combination of spiraling motion and rotation and the centre we talk about here is the centre of that spiralling motion. This centre starts ahead of the aircraft (and to the side, since the spin is to one side of the flight path before stall) and is closer to the aircraft for flatter spins.
Note that this means there is both torque, making the plane rotate, and an unbalanced lateral (centripetal) force, making it turn around.

From my personal experience, when I do a stall spin to the right my body wants to move forward and to the left of the airplane. That would indicate that the center of rotation is right of the center of mass and no longer in the symmetry plane.


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Would a pure flying wing in straight and level flight have zero wing bending stress?
In studying the NASA 247 foot wingspan solar powered Helios aircraft it seemed that evenly spacing the weight would help create a lower bending stress across its span when in flight, as gravity and lift forces would cancel each other out more evenly as compared to a single fuselage.
The Helios did have spaced pods slung underneath, but none at the ends.  The aircraft, in turbulence (perhaps an updraft) that caused its wingtips to bend upwards, started a pitch up/pitch down cycle until the wing failed.  Could more even spacing of weight on the wing reduce the possibility of this happening again?

You're still using terminology incorrectly.  "Net wing loading" isn't a weight/lift vector sum, it's simple weight per unit area, that has to be offset by lift.  Span loading decreases wing flexing moments, it does nothing to change wing loading.

Edited to reflect more proper "span loading" concept.

Does your last edit invalidate the existing answers? It does seem so at first glance, since none of them reference bending stress. Note that this is highly discouraged on this site.

I actually wanted to delete the question.  I have learned much since last year.

Net wing loading (weight per unit lifting area) can't be zero in level flight.  Lift must equal weight, else the aircraft will accelerate in the direction of the net force.
The loading distribution on the Helios is designed to reduce flexing moment along the span, which is an entirely different thing.  As you note, that optimization wasn't perfect, although pitch oscillation wasn't necessarily related to the wing flex that shows in the video.

weight and aerodynamic lift forces will only cancel out (0 net loading)

Lift and weight cancel out when their vector sum is zero. I.e. $W + L = 0$.
However, wing loading is the ratio of their magnitudes, $\frac{|L|}{|W|}$. Since from the previous equation we have $L = -W$, we can substitute $\frac{|L|}{|W|} = \frac{|-W|}{|W|} = \frac W W$ and trivially see that when weight and lift cancel out, the wing loading is $1$.
This is case whenever the aircraft is flying straight and level, at any speed.
The only situation when the net loading is zero is when lift is zero, which means it is flying along a free-fall trajectory.


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What are the effects of adding power to a 45 degree banked aircraft?
In a recent question it was proposed that adding excess power to an aircraft in a level 45 degree banked turn would cause it to pitch up into a rolling climb.
This case was compared with level flight using a positive static stability (CG forward-tail down force) model.
In level flight, adding excess power will initially cause an increase in speed, followed by increase in tail downforce,  followed by a pitch up, followed by speed stabilization and climb.
Pitch controls speed, power controls altitude.
Roll 45 degrees and do a level coordinated turn around a point. Add in power.
What I am seeing is a turn around a barber pole with no change in roll, an ascending spiral.
If we added more pitch,  leaving the throttle, rudder and ailerons where they were, a slower upward spiral with steeper barber stripes?
The plane does not seem to roll, the wing is always pointed to the same pole.
Is there any rolling motion WRT aircraft performing these manuvers?

Well you have torque and slipstream effects, which are both causing yaw and reducing trim speed, complicating things.  In flight you will be making subtle changes to control inputs to hold the bank angle almost unconsciously, and if you don't it'll wander off on its own soon enough.

"But the plane never rolls, the wing is always pointed to the same pole.." if your nose is really high, say 60 degree climb angle, and your left wing always points to the barber pole, you will be rolling a lot.

@Mike Y Let's call it orbiting.  I believe there is a roll effect see answer below.

Well. If you add power, the first thing that happens is the aircraft gains speed. This widens the turn. Then it pitches up (meaning up and inward, as aerodynamic “up” is rotated 45°). So now - are we still coordinated here?

@Cpt Reynolds "The radius widens" yes.  Then it pitches up (speed decreases, radius decreases). "are we coordinated" if rudder and aileron are unchanged, and airspeed remains the same, Yes? (But now we are in a climbing spiral).

Barber pole?  Unclear what this means.

@Carlo Felicione that would be the inside wing tip tracking the stripes on a barber pole (a climbing turn around a point).

The key is that you qualified the turn as coordinated.  If the turn continues coordinated after the application of more power, then the aircraft will climb due to increased energy being converted to altitude.  Unless you decide to "lower the nose" and turn at a faster airspeed.

I did not address rolling.  There are many aspects of your questions, and I thought I would address perhaps the most important first.

Learning the physics might be accomplished in a different manner. A starting book on practical aerodynamics which I send primary students to, as well as CFI candidates, is by John Denker, https://www.av8n.com/how/    Take a look at that.  If you are motivated, just start at the beginning and work your way through the book.

From my perspective there are several interrelated questions, for which an effective answer would either require prerequisite knowledge and understanding, or a tutorial, which is beyond the scope of comments.  So I suggested the source so that you could increase your knowledge base.  In any engineering/scientific inquiry there are different thought models which can be used to explain things, and the referenced book answers most of your questions in one or more of those models.  That is why I suggested it. In general, a single question may get a better answer, but you might have to bound it.

I will rephrase the question.

Could not see a roll in an orbiting aircraft, but so many experienced people said there is a difference in roll force in an ascending or descending turn.  Outside wing has greater angle of attack?
After running the simulation in my mind many times, it occurred to me that vertical velocity ascending vs descending will create an opposite effect on the TAIL, more specifically, the vertical stabilizer.  If it is canted over to 45 degrees, an increase in vertical velocity (say from 0 feet/sec to 5 feet/sec) will create a rolling force!
Another source of roll in a pitch up would be the aileron input required to overcome dihedral stability effect, which is strongest when the plane is in horizontal flight.  As it pitches up, the lift differential caused by rolling is less and less. One would have to "roll toward the high wing" to compensate.  But the effect would be same in a dive, not opposite.  However, it would not be transient, and would increase as pitch increases.
These effects may be part the mystery.  An orbiting plane does not roll in a constant turn around the point, but if it changes pitch rolling forces may be created.

I think it’s kind of important to define which effects you want to consider and which not. Is thrust assumed to be a point vector? Do you consider propeller slipstream? What about rudder effects to counter prop torque? Once these all are considered, it becomes an aircraft-by-aircraft question, not a theoretical generic exercise in flight mechanics...

I’m not sure I get what you mean... are we considering prop effects and the likes, or is thrust balanced in pitch, roll and yaw in our assumptions?

@Cpt Reynolds I was actually modelling with an F16 to try to eliminate these factors and stick to the maneuver itself.  There is agreement that a turn around a point has no roll.  I was (laughing a bit) as to what would happen is you applied full thrust.  Wound up worrying about G forces.

Huh? I second the Cpt., I have trouble following the line of thought you are trying to convey here.

@RobertDiGiovanni -- re "Could not see a roll in an orbiting aircraft, but so many experienced people said there is a difference in roll force in an ascending or descending turn."-- you are confusing the geometrical fact of a non-zero roll rate, with a statement about roll torque.  They are not the same.

@quiet flyer saw your video, thanks.  Now to fly that maneuver you would eliminate yaw, add power, pitch up, and roll.  A few changes.  Now what you did not do is maintain the radius of your turn (or make it larger with increased speed). Does not apply here, but excellent (liked the design of your plane too).

@Cpt Reynolds I see the point that other factors, some which may cancel each other, can affect the net forces on a plane if a change is made, for example, tip speed differential decreases as roll increases in a turn, P factor and slip stream increase with throttle change.  What I am searching for is if there is any roll in a steady state climb around a theoretical barber pole.

What I am seeing is a turn around a barber pole with no change in roll, an ascending spiral.

Here’s a way to see that in an ascending spiral, you must have some roll, along with some pitch and yaw.
Take your model airplane by the wingtips and hold in an angle of bank with some nose up, so it is in the position of an ascending spiral. Now give it a wee little bit of yaw, which will drop the nose. Give it enough rotation about the wingtips (pitch) to return the nose to the set angle above the horizon. Keep repeating this, being careful not to add in any roll. You are simulating a simultaneous yaw and pitch without roll.
Watch what the angle of bank does.

In order to simulate simultaneous rotations about two or three axes, you need to do it in small, little increments. Like, a degree or two at a time. A little yaw, a little pitch. Try it.

Thank you so much for staying with it!  A plane sets its roll and "turns" around a circle with its wing!  The maximum roll component of an orbit is...1 roll per orbit if the same wing points to the "pole".  The plane would have to be flying with its nose almost straight up (using some of its thrust to continue the circle like a helicopter) and the plane slowly rolling to stay pointed. An average GA plane would orbit a 0.5  mile radius in around 1.5 minutes, giving a roll rate at around 90 degrees pitch of 0.66 rolls per minute.

The key is to keep the radius of the circle constant.  Modelling an ever tightening circle confuses the roll component of orbiting object with other factors.  In reality, it is real, but relatively insignificant.  I realized that thinking how the moon keeps the same side towards the earth.  It "rolls" every 30 days! But it is real, and thanks for making me more aware of it.